Superconducting alternator



May 17, 1966 1. 1A DRAUTMAN SUPERCONDUCTING ALTERNATOR Filed Dec. 3,1962 INVENTFH?.

JAMES J. DRAUTMAN BYUWQ:

ATTORNEY United States Patent Ofce 3,252,018 Patented May 17, 19663,252,018 SUPERCONDUCTING ALTERNATOR James J. Drautman, Jamison, Pa.,assignor to Malaker Laboratories, Inc., High Bridge, NJ., a corporationof New Jersey Filed Dec. 3, 1963, Ser. No. 327,613 4 Claims. (Cl. S10-16) This invention deals with an al-tematir operating undersuperconducting conditions. More specifically, it relates to asuperconducting alternator, particularly of the miniature type, anddesigned to utilize the principle of flux compression inmultiply-connected superconductors.

When a multiply-connected superconductor, such as a cylindrical shellmade of superconducting material, is cooled below its transitiontemperature in the presence of a magnetic field, the flux enclosed bythe superconductor is trapped, and it remains constant, even though theexternal field may be reduced to zero. If a superconductor is cooledbelow its critical temperature in a zero magnetic field, the eld cannotpenetrate beyond a small depth known as the penetration depth.

According to this invention, it has been found possible to trap amagnetic fiux within a multiplyonnected superconductor, and 'then toinsert a' superconducting piston, which has been cooled to below itscritical temperature in a zero magnetic field. Since the liux canneither penetrate this piston, nor escape from the core, thecross-sectional area available for the flux is reduced, so that themagnetic field must rise correspondingly. By employing an armature woundaround the interior of the cylinder, and a solenoid coil wound aroundthe exterior, hight ux densities can be obtainable. Reciprocation of thepiston thus produces an alternating current generator having areasonably high output. In order to trap the flux in the generator afterthe superconducting materials have been cooled below their transitiontemperatures, a switch, made of heater wire wound around a core, isutilized. Since in normal operation the alternator is cooled below itstransition temperature before the magnetic field is applied, the switchis utilized to permit flux to intially penetrate the cylinder by drawinga portion of the cylinder conventionally.

The invention will be more readily understood by refer ence to theaccompanying drawings in which a preferred embodiment is described, andin which FIGUR'E l depicts a cross-sectional view of amultiply-connected superconductor, while FIGURE 2 illustrates across-sectional side view of a multiply-connected superconductorprovided with armature and solenoid and a reciprocating superconductingpiston. FIGURE 3 presents a cross-sectional side view of asuperconducting alternator of the present invention. Similar numeralsrefer to similar parts in the Now, if a superconducting piston 5 wereinserted in opening A1, men

Where represen-ts the compressed flux, B is the compressed field, and ADis the area taken up by the piston 4. Since the total flux cannotchange, and

Bo Ari-(Ar-AP) This latter relationship is valid as long as B' is notgreater than the critical field forv the superconducting material used,at the temperature of operation. Materials have been developed recentlywhich are capable of remaining superconducting in fields of 200,000oersteds.

An electrical generator of the present invention utilizes the aforesaidprinciple of flux compression. As shown simply in FIG. 2, it employs amultiply-connected superconductor 4 having an externally-wound solenoidcoil 6, wound in insulating relation around conductor 4, and an armature7, similarly wound along the inner wall of conductor 4. -Piston 5, alsomade of superconducting material, is reciprocated within said armature.It is to be understood that coils 6 and 7, Ifor the purposes of thepresent invention, may be made of conventional material or ofsuperconducting material. The latter, of course, is preferred, due tothe fact that the unit may be made of small size, yet high magneticfields may be employed so as to produce relatively high outputs.

As is apparent from FIG. 3, the alternator, indicated generally bynumeral 8, is enclosed in a Dewar ask 9, having vacuum space 10 betweenits walls. The liask 9 is filled with a cryogenic liquid, such as helium1:1. The generator 8 consists of superconducting solenoid 6 designed toproduce the intial field B0. The core of the solenoid is asuperconducting hollow cylinder 4 having a wall thickness greater than0.127 X 10-3 inches, which is the penetration depth for a magnetic fieldin the material used (in this case Nb+25% Zr). An armature 7, alsopreferably of superconducting material, is wound around the interiorwall of cylinder 4, and its leads l2 and 13 serve to remove the outputpower of the alternator 8. It will be noted that flask 9 is providedwith permeable cover 14 through which the various leads are drawn, ininsulating relation therewith. Power for the solenoid coil 6 is fed inthrough leads 15 and 16. superconducting piston 5 reciprocates withinarmature winding 7, and it is provided with rod 17 which passes throughflask cover 14 via a flexible bellows connection 18. Piston rod 17 isreciprocated by an external source (not shown).

`By using the superconducting solenoid, high fiux densi- -ties can beobtained with minimum size and weight of components. Since it isdesirable, if not necessary, to charge the generator with coolant priorto use provision must be made to trap the fiux in the generator afterthe superconducting materials have been cooled to below their transition(critical) temperatures. According to this invention, a novel switch isemployed, consisting of a few t-urns of heater wire (e.g., resistancewire scid as Nichrome") wound lengthwise the core, such as wire 19 woundin insulating relation lengthwise of core 4, around the cylindrical wallthereof, the Vterminal ends 20 and 21 of the wire being connected to asource of current for heating the wire when liux trap control isnecessary. When this heater 19 is energized, a cross section of core 4then is no longer superconducting or multiply-connected, and can beconsidered as being driven as normal, so that the ux then can penetratethe core. When the heat is turned off from switch" 19, the flux becomestrapped within the core.

When in operation, the flask 9 is cooled with cryogenic liquid, suchliquid helium, the temperature of which is below the transitiontemperature of the superconducting materials used. Solenoid coil 6 thenis energized by passing direct current through 15 and 16, whereby core 4becomes magnetized. A superconducting switch, indicated generally as 22,ispu-tilized so that, once solenoid coil 6 has been energized, themagnet 4 becomes a part of a su'perconductingloop, and the externalpower source at leads 15 and 16 can be disconnected. Switch 22 consistsof a superconducting wire 23 wound with a few turns of heater wire 24which are `energized via leads 25 and 26. The ends of cylinder 23 areconnected across leads 15 and 16 at points 27 and 28 in the cryogenicliquid. lt is to be understoodthat heater wire 24 need be only adequateto heat a portion of wire 23 to above its critical temperature, where itis no longer superconducting, when such switching is required.Thereafter, the flux trapping switch 19 isenergized so that ux canpenetrate generator core 4. This switch" then is turned olf, trappingthe flux.

When piston 5 (also made of superconducting material) is reciprocated upand down within core 4, an alternating current is generated in arma-ture7, and this current may be drawn olf through leads 12 and 13. Actually,the magnetic field expels piston 5 from core 4, so that energy is neededonly to pull the piston back into the center.

The voltage induced in armature 7 may be indicated by the followingrelationship:

Where V is the voltage, 4 the llux, and t is time. By neglecting endeffects, and assuming the field to vary linearly with time, we obtainthe followin-g relationship:

i- 3 0 s V- nA At X 10 Where n is the number of tums of solenoid 6, A isthe cross-sectional area, in crn.3 of magnet 4, B, is the compressedeld, in gauss,'after piston 5 has entered the magnet, B is the originaleld when piston 5 is removed, in gauss, and t is the time, in seconds,for one cycle.

Using a cm. long magnet with a 2 cm. LD., and a 1.8 cm. diameter piston,

So that, from an initial lield of l kg., Bl is 2.76 kg. With a 1000 turnarmature, and an operating frequency of 60 cycles,

V=3.3 volts The losses, as estimated from the data on wires made ofNb+25% Zr, are as follows:

For a field of 3 kg., and 60 c.p.s., the loss would be:

P/m=2.6x l0-u watts/gm.

From the foregoing, it is seen that a useful and novel low powerelectrical generator has been devised, utiliing the principle of fluxcompression is multiply-connected v oRIs L. KADER, Primary Examiner.

superconductors. Use of such a generator permits extreme miniaturzation,while at the same time significant power outputs may be obtained.

I claim:

1. vA superconducting electrical generator, comprising,

a hollow cylindrical shell made of superconducting material and designedto become a superconductor when cooled to below its transitiontemperature,

a conductive coil wound around the outside of said shell, therebyforming a solenoid,

a conductive coil wound around the inside of said shell and serving asan amature, and having output leads at its ends, and

a piston made of superconducting material and designed to bereciprocated within said armature coil, and designed, when reciprocated,while said generator is under superconducting conditions, to induce analterhating current in said armature coil, which current may be drawnout through said armature coil leads.

2. A superconducting electrical generator, according to claim 1, inwhich a heater wire is wound around said shell, serving as a ux trapswitch when energized to heat a portion of said shell to above itstransition temperature.

3. A superconducting electrical generator, according to claim l, inwhich a length of superconducting material is connected, inshortdcircuiting relation, across the solenoid coil leads subjected tosuperconducting conditions, and a heater wire wound around said length,serving ns a ux switch when energized to heat said length to above itsItransition temperature.

4. A superconducting electrical generator, comprising,

an insu-lated vessel designed to contain a cryogenic coolam capable ofrefrigerating to below the superconducting transition temperature of thesuperconducting generator,

a hollow cylindrical shell made of superconducting material anddisposable in said vessel,

a coil made of superconducting material and woind around the outside ofsaid shell, thereby forming a solenoid,

-a coil made of superconducting material and wound around the inside ofsaid shell, and servin-g as an armature and having output leads at itsends,

a piston made of superconducting material and designed to bereciprocated within said armature coil, and designed when reciprocated,while said generator is under superconducting conditions, to induce analtemating current in said armature coil, which cur- 'ent may be drawnout through said armature coil eads,

a heater wire wound around said shell and serving as a lux trap switchwhen energized to heat a portion of said shell to above its transitiontemperature,

a length of superconducting material connected in shortcireuitingrelation across said solenoid coil leads subjected to superconductingconditions, and

a heater wire wound around said length and serving as a flux switch whenenergized to heat said length to above its transition temperature.

No references cited.

D. F. DUGGAN, Assistant Examiner.

4. A SUPERCONDUCITN ELECTRICAL GENERTOR, COMPRISING, AN INSULATED VESSELDESIGNED TO CONTAIN A CRYOGENIC COOLANT CAPABLE OF REFRIGERATING TOBELOW THE SUPERCONDUCTING TRANSITION TEMPERATURE OF THE SUPERCONDUCTINGGENERATOR, A HOLLOW CYLINDRICAL SHELL MADE OF SUPERCONDUCITING MATERIALAND DISPOSABLE IN SAID VESSEL, A COIL MADE OF SUPERCONDUCTING MATERIALAND WOUND AROUND THE OUTSIDE OF SAID SHELL, THEEBY FORMING A SOLENOID, ACOIL MADE OF SUPERCONDUCTING MATERIAL AND WOUND AROUND THE INSIDE OFSAID SHELL, AND SERVING AS AN ARMATURE AND HAVING OUTPUT LEADS AT ITSENDS, A PISTON MADE OF SUPERCONDUCTING MATERIAL AND DESIGNED TO BERECIPROCATED WITHIN SAID ARMATURE COIL, AND DESIGNED WHEN RECIPROCATD,WHILE SAID GENERATOR IS UNDER SUPERCONDUCTING CONDITIONS, TO INDUCE ANALTERNATING CURRENT IN SAID ARMATURE COIL, WHICH CURRENT MAY BE DRAWNOUT THROUGH SAID ARMATURE COIL LEADS, A HEATER WIRE WOUND AROUND SAIDSHELL AND SERVING AS A FLUX TRAP SWITCH WHEN ENERGIZED TO HEAT A PORTIONOF SAID SHELL TO ABOVE ITS TRANSITION TEMPERATURE, A LENGTH OFSUPERCONDUCTING MATERIAL CONNECTED IN SHORTCIRCUITING RELATION ACROSSSAID SOLENOIL COIL LEADS SUBJECTED TO SUPERCONDUCTING CONDITONS, AND AHEATER WIRE WOUND AROUND SAID LENGTH AND SERVING AS A FLUX SWITCH WHENENERIGIZED TO HEAT SAID LENGTH TO ABOVE ITS TRANSITION TEMPERATURE.